1. Field of the Invention
The present invention relates to a planar inverted F antenna (PIFA) for wireless communication devices such as wireless modems, cellular telephones, personal digital assistants, etc. More particularly, the present invention relates to the method of mechanically tuning the resonant frequency and/or the antenna input impedance of the antenna.
2. Description of the Related Art
A planar inverted F antenna continues to be used in various wireless communication devices, which are made in different packages using different printed circuit boards (PCBs). This means that the antenna has to be redesigned for every single application, thus reducing the benefits of high-volume manufacturing. However, if there was a way of mechanically tuning the same basic antenna design to the different package/PCB combinations, then that same antenna design could be used in various applications with reduced unit cost of manufacturing it. To the best of applicants"" knowledge, no such mechanical tuning mechanisms for PIFA antennas have been proposed so far.
A method of tuning a PIFA antenna by adjusting the volume and proximity of a dielectric material to the feed and shorting pins and/or capacitive-loading plates of the antenna is described. The present invention permits the antenna to be tuned to suit variations in applications such as where the ground plane varies in size or where there is a frequency shift required due to the different materials used to make the chassis in which the antenna is mounted. In one embodiment of the invention, the PIFA antenna includes a movable tuning member in the form of a selectively rotatable rotor having a semi-circular rotor vane provided thereon. In another embodiment, a selectively movable block or slug is utilized as the movable tuning member. In still another embodiment of the invention, the frame which supports the movable tuning members in the other embodiments has a slot molded thereinto. The size and position of the slot can be altered, thereby providing a range of antennas based on the same patch and mold tool.
A principal object of the invention is to provide a means of selectively varying or changing the resonant frequency and/or input impedance of an antenna without having to redesign and make a new antenna.
A further object of the invention is to provide a single antenna which can cover a wider frequency range than was previously available.
Still another object of the invention is to provide an antenna wherein it is possible to replace a number of antennas with a single selectively variable design, thereby reducing unit cost in volume manufacturing as well as the antenna design time.
These and other objects will be apparent to those skilled in the art.